In an optical module in which light from a laser device is directly introduced (i.e., optically coupled) into an optical fiber, the laser device and the optical fiber must be centered and aligned with respect to each other in order to increase optical coupling efficiency. This alignment process can be accomplished in two ways: passive alignment in which the relative position between the laser device and the optical fiber is adjusted by reference to a preset alignment mark, and active alignment in which the laser device is caused to emit light and the relative position is adjusted while monitoring the light output coupled into the optical fiber. Generally, the active alignment process can achieve highly precise alignment compared with the passive alignment process, but the fabrication cost of the active alignment process is higher because the alignment process takes time.
In view of the above, optical modules have been proposed that are simple in structure and yet can achieve high optical coupling efficiency comparable to that of the prior art active alignment. For example, patent document 1 discloses an optical module in which an LD (laser diode) mounting substrate with an LD mounted on a surface thereof is mounted on a guide substrate provided with a guide groove holding an optical fiber and a concave groove connecting to an end portion of the guide groove, in such a manner that the LD is accommodated within the concave groove. In this optical module, the vertical alignment between the optical fiber and the LD is performed by passive alignment, while the horizontal alignment is performed by active alignment.
In an optical module that uses an optical device such as an LD, the device must be hermetically sealed and protected against infiltration of external moisture, etc., in order to stabilize the characteristics of the device and to improve its reliability. In particular, in the case of a laser device that emits light at a relatively short wavelength, such as blue, the device must be hermetically sealed in order to also prevent accumulation of impurities on the light emitting part, because such a laser device is susceptible to absorption effects by light energy. In view of this, a hermetic sealing structure of an optical module is proposed in which a substrate on which an optical device and an optical fiber are mounted is hermetically sealed by means of such as solder or adhesive.
For example, patent document 2 discloses a hermetic sealing structure of a waveguide-type optical device in which an optical waveguide is formed within a first substrate and an optical fiber is optically coupled to the optical waveguide. In this optical device, a second substrate, on which a first groove is formed at least in a region thereof that opposes an optical waveguide pattern defining the optical waveguide, is bonded in such a manner as to align the groove pattern with the optical waveguide pattern formed on the first substrate.